Plain English Meaning
It is a stall flown the way you would set up for landing — engine pulled back, flaps and gear out — so you learn to recognize and recover from a stall in the conditions where one is most likely to happen on final approach.
Full Definition
A stall practiced or encountered with the engine at idle or a low power setting, simulating the aerodynamic conditions of a normal approach to landing. The airplane is configured for landing (gear down if applicable, flaps extended), and back pressure is progressively increased until the wing exceeds its critical angle of attack and stalls.